New VIMS research questions toxicity of Pfiesteria
shumwayae
Researchers at the College of William and
Mary's Virginia Institute of Marine
Science (VIMS) have found that Pfiesteria
shumwayae, a member of the toxic
Pfiesteria complex (TPC), kills fish
by feeding directly on their skin, not
by releasing a potent toxin into the water,
as has been widely reported.
The findings are published in this week's
issue of the journal Nature.
VIMS researchers investigated the
pathogenicity of P. shumwayae using an
innovative larval fish bioassay developed at
the Institute. "This bioassay allows us
to investigate the interaction between
Pfiesteria and fish in great detail,"
says Dr. Wolfgang Vogelbein, the Nature
article's lead author. Using a
P. shumwayae culture known to kill
fish, the scientists performed controlled
fractionation studies in which they used
centrifugation and filtration to remove the
dinoflagellates from the water, presumably
leaving any toxin(s) the organisms may
have secreted. They also used permeable
membranes to separate the dinoflagellates
from the fish during exposure studies. "Only
in treatments where fish were in direct
physical contact with the dinoflagellate did
we see fish dying," says Vogelbein.
Further evidence against secretion of a potent toxin by P.
shumwayae comes
from observations of the dinoflagellate and
fish using videomicrography,
high-resolution microscopy, and electron
microscopy. "Direct observation of the
assays with microscopy allowed us to observe
dinoflagellates in large numbers swarming
toward the fish and rapidly attaching and
feeding directly on the fish skin," says
Vincent Lovko, a VIMS graduate student who
helped to develop the new bioassay.
"Standard bioassay methods used by others
cannot distinguish between toxigenicity
and killing by micropredatory feeding," says
Vogelbein. The VIMS researchers thus
recommend that all strains and species of
Pfiesteria be reevaluated for
toxicity using these sensitive new methods.
"This is the only way to determine if
there are, in fact, any bona fide
toxic strains out there," Vogelbein says.
The role of Pfiesteria in aquatic
animal and human health remains
controversial. "This new research clearly
demonstrates that
Pfiesteria shumwayae, even though it
does not secrete any potent toxins, can
kill fish in closed systems, under controlled
laboratory conditions," says Dr. Jeffrey
Shields, another co-author of the Nature
article. "Does Pfiesteria do this in
the natural environment? That question
remains to be answered."
The new research has important
implications for scientists trying to understand
both the basic biology of Pfiesteria
species and the possible role these
dinoflagellates may play in estuarine fish
kills and fish-lesion events.
The findings are important to government
agencies charged with protecting
environmental and human health. Research
efforts designed to answer these questions
continue at VIMS, with grant support from
EPA, NOAA, and the Centers for Disease
Control and Prevention.
|
